A fresh batch of copies of Pirkei Avot: A Users' Manual has been printed. With a favourable breeze behind them, they should reach the shores of the United States before the end of August. Once they get there, they will be distributed by Ktav and it will be possible to purchase them via Amazon as well as in some bookshops.
Copies that have reached the UK can now be bought online, through Amazon UK. The Amazon seller is Judaism Reclaimed. You can access the sales page by clicking tinyurl.com/mtsdp8n3 and then waiting a few seconds for the "other options" panel to open up. There you will find Pirkei Avot: A Users' Manual on sale at the price of £70 for the three volume set.